This application is related to copending applications U.S. Ser. No. 08/103,947, filed Aug. 10, 1993, titled CONTROL SYSTEM/METHOD FOR ENGINE BRAKE-ASSISTED SHIFTING and U.S. Ser. No. 08/179,060, filed Jan. 7, 1994, titled ENGINE BRAKE-ENHANCED UPSHIFT CONTROL METHOD/SYSTEM, and assigned to the same assignee, EATON CORPORATION, as this application.
The present invention relates to a system and method for decreasing the time required to complete a ratio change in an electronically enhanced engine and transmission system.
Electronically enhanced transmission systems have been well developed in the prior art as may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,595,986; 4,648,290; 4,722,248; and 5,050,427, the specifications of which are hereby incorporated by reference in their entirety. Transmission systems such as these have been utilized to provide a variety of gear ratios to enhance the flexibility and torque multiplication of an engine to service a plethora of applications. The most common applications include MVMA Class 7 and Class 8 tractor semi-trailer vehicles although other applications, such as automobile or stationary power plant powertrains, may also be serviced.
Art electronic control module which includes a microprocessor is often used to control the powertrain, which includes an engine as well as a multiple gear ratio transmission. The continuous evolution of microprocessor technology has enabled increased accuracy and expanded the scope of control over engine and transmission operations. The electronic control module collects data from various sensors and issues commands appropriate for the current operating conditions to control the engine and transmission. Engine control may include modulating fuel, operating engine accessories, or managing application of an engine brake or driveline retarder. Transmission control may include selection of an appropriate gear ratio, including disengagement of the current gear ratio and engagement of a new target gear ratio, or operation of an input shaft brake.
Efficient ratio changing improves fuel economy and enhances drivability of a vehicle. Under certain demanding situations, such as when negotiating a steep grade with a heavily loaded vehicle, swift ratio changes are required to prevent the vehicle from losing momentum and missing the window of opportunity to complete the shift entirely. Under normal driving conditions, an operator may have to shift gears more than fifteen times before reaching highway speeds. In these applications, inefficiency in ratio changing may accumulate to a significant amount of wasted time. Thus, it is desirable to reduce the time necessary to complete a ratio change or shift.
A typical ratio change involves a number of steps. First, the operator must interrupt the transfer of torque from the engine through the transmission to the driveline. This may be accomplished by disengaging a master clutch which provides a frictional coupling between the engine and the transmission. Alternatively, a xe2x80x9cthrottle dipxe2x80x9d may be performed where the throttle is abruptly decreased. Once the torque transfer has been interrupted, the current gear is disengaged and the transmission is in a neutral state.
The next step in a typical ratio change involves selecting the target gear ratio. This may be the next available gear ratio in the sequence, or a number of available ratios may be skipped, depending on the current operating conditions. Before engaging the target gear, the transmission input shaft should rotate at a substantially synchronous speed for the current output shaft speed and target gear ratio. When the master clutch is engaged, the input shaft speed may be controlled by controlling engine speed since the engine and transmission are coupled. Engine speed may be increased (for a downshift) or decreased (for an upshift) to realize synchronous speed. On transmissions equipped with an input shaft brake, the input shaft speed may be reduced by disengaging the master clutch and applying the input shaft brake (also known as an inertia brake or clutch brake). However, input shaft brakes with sufficient capacity to decrease ratio changing time add cost and complexity to the transmission system and require accurate sequencing of events for satisfactory operation, so many transmissions only utilize simple versions of these devices.
For transmissions without input shaft brakes, synchronous speed will not be attained with the master clutch engaged on an upshift until the engine speed naturally decays to synchronous. As engines become more and more efficient, the reduction of internal frictional losses results in a substantially lower natural engine decay rate. This results in a correspondingly longer time to complete a ratio change. Thus, it is desirable to increase engine deceleration during an upshift to achieve synchronous speed shortly after disengagement of the current gear.
A device often utilized to provide a variable retarding force to an engine, is an engine brake. The most common engine brakes may be either engine compression brakes or exhaust brakes. These devices are well known in the prior art and are commonly provided on heavy-duty vehicles. Examples of vehicular automated mechanical transmission systems utilizing engine brakes may be seen by reference to U.S. Pat. Nos. 4,933,850 and 5,042,327 the specifications of which are hereby incorporated by reference in their entirety.
Engine compression brakes are usually manually operated and provide a variable retarding force resisting engine rotation by altering valve timing of one, two, or three banks of cylinders. This creates compressive force within the cylinders which resists rotation of the crankshaft. Exhaust brakes operate in a similar fashion by restricting exhaust flow from the engine. Exhaust brakes do not offer the responsiveness or flexibility of engine compression brakes although they are less expensive to employ.
Traditionally, engine brakes are utilized to assist the vehicle service brakes by supplying a resisting torque on the driveline when descending long grades. Manual operation of the engine brake in these situations continues to be a desirable option. More recently, engine brakes have been manually operated to decrease the time required for ratio changes. For this application, manual operation of the engine brake often results in large torque disturbances to the vehicle driveline due to inappropriate timing in applying and releasing the engine brake. This reduces drivability of the vehicle and may also adversely affect the durability of powertrain components. Furthermore, proper operation is largely dependent upon the skill and experience of the vehicle operator.
It is, therefore, an object of the present invention to provide a system and method for reducing the time required to complete a ratio change, in particular, an upshift ratio change, in a manual, semi-automatic or fully automatic transmission.
It is an additional object of the present invention to provide a system which reduces the time required to achieve synchronous speed by increasing a retarding force acting on engine rotation.
Another object of the present invention is to provide a system which automates control of an engine compression brake to decrease ratio changing time in a manual, semi-automatic or fully automatic transmission.
A still further object of the present invention is to provide a system which increases engine load to supply a variable retarding force so as to improve ratio changing times in a manual, semi-automatic or fully automatic transmission.
Yet another object of the present invention is to provide a system which reduces driveline disturbances during an upshift by utilizing an engine brake when a transmission neutral condition is sensed.
In carrying out the above object and other objects and features of the present invention, a control system is provided for reducing the ratio changing time of a mechanical transmission system. The transmission system includes an engine selectively coupled by a master friction clutch to a mechanical change gear transmission. The system also includes an electronic control unit for receiving a plurality of input signals indicative of an engine speed, an output shaft speed, and a neutral gear state of the transmission. The electronic control unit also generates command signals for controlling the engine and the transmission. The transmission includes a plurality of gear ratio combinations, and a neutral gear state, selectively engageable between a transmission input shaft and a transmission output shaft. The control system utilizes a sensor for sensing the neutral gear state which occurs after disengaging a current gear ratio and before effecting a target gear ratio in the transmission. The system also includes devices for applying a retarding torque to the engine in response to a command from the electronic control unit. The retarding torque is applied to the engine while the engine speed is above the synchronous speed at which the target gear ratio is effected, so as to increase engine deceleration and reduce ratio changing time. A method is also provided for use with the system and similar systems.
The above objects and other objects, features, and advantages of the present invention will be readily appreciated by one of ordinary skill in the art from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.